1NVERTEBRATA. 



339 



It begins with a small buccal chamber (in somites 1 and 2) 

 without jaws or any other hard structures, and this is fol- 

 lowed (in somites 3 to 5) by a strong muscular pharynx, and 

 this by an oesophagus (somites 

 6 to 12). Into this a fluid is 

 poured from three pairs of 

 calciferous glands (somites 10 

 to 12), the first of which are 

 hollow, the other solid. The 

 fluid contains minute crystals 

 of calcium carbonate, and its 

 function is to neutralize the 

 organic acids always present 

 in the soil which is eaten. 

 Behind the oesophagus is a 

 dilated portion called the crop 

 (somites 13 to 16); this is 

 followed by a strong muscular 

 crushing gizzard (somites 17 to 

 19). All the rest of the canal 

 is intestine, not differentiated 

 into regions. It is lined by 

 a glandular epithelium sur- 

 rounded by a layer of vascular 

 connective tissue. These two 

 layers are infolded on the 

 dorsal side to form a longitu- 

 dinal typhlosole (fig. 175). 

 There is also a thin muscular 

 layer, and finally the coslomic 

 epithelium. This latter is 

 specially modified on the ex- 

 terior of the intestine, and 

 to a less extent farther forward, giving rise to a yellow 

 tissue, which has been called chloragogen tissue. This 

 term appears to mean green-excreting, the term chloros 

 in Greek meaning yellowish-green. It has been shown 

 that this tissue contains uric acid and also glycogen, so 

 that it would appear to perform two of the functions of 

 the vertebrate Uver. 



Fig. 176. ALIMENTARY CANAL OF 

 EARTHWORM. 



Dorsal view of anterior portion. 

 (After Howes). 



